Table Of ContentADVANCE PRAISE FOR FIBER FUELED
“Will is Dr. Fiber! Get on the fiber train and transform your health from the inside out, literally. . . . Poop
like a champ, build an immune system that is a fortress, and feed your brain premium-grade fuel. Pick up a
copy of Fiber Fueled today!”
—Rip Esselstyn, New York Times bestselling author of The Engine 2 Diet
“This book is a timely and authoritative discussion of the overwhelming scientific evidence supporting the
health benefits of a largely plant based diet. It focuses on the role of fiber, a key element of plant-based
diets, and presents this ancient wisdom from the perspective of modern microbiome science. A must-read
for everybody still unconvinced about the best diet to stay healthy.”
—Emeran A. Mayer, MD, PhD, author of The Mind-Gut Connection and Distinguished
Professor of Medicine, Physiology and Psychiatry, David Geffen School of Medicine at UCLA
“The gut microbiome is the engine that drives the body to health and today’s diet is deficient in its preferred
fuel: fiber, the elixir of life. Instead, we are overfed, undernourished, and overmedicated. Fiber Fueled is a
must-have owner’s manual revealing the secrets for gut and total body health. Read Dr. Will Bulsiewicz’s
groundbreaking book today!”
—Gerard E. Mullin, MD, MS, author of The Gut Balance Revolution and Director of
Integrative GI Nutrition Services, Johns Hopkins Medicine
“Like the microbes in our gut, Dr. Bulsiewicz helps us digest a large quantity of complex material. Fiber
Fueled translates the latest cutting-edge science of the gut microbiome into accessible and practical
information. This is required reading whether you are interested in a heathier gut and body or learning about
one of the most transformational fields in biomedicine.”
—Justin Sonnenburg, PhD, author of The Good Gut and Associate Professor, Stanford
University
“If ‘all disease begins in the gut’ as Hippocrates said, then all health begins there too. Dr. Bulsiewicz and
the Fiber Fueled 4 Week Plan are the natural jumpstart to feeding our gut its preferred and premium fuel.
This book is the answer for so many of my patients searching for a higher level of wellness.”
—Joel Kahn, MD, FACC, author of The Plant-Based Solution and Clinical Professor, Wayne
State University School of Medicine
“Drawing on his vast experience as a practicing gastroenterologist, Dr. Bulsiewicz illuminates a path to
optimal gut health using ‘food as medicine’ to unleash the incredibly powerful, absolutely fascinating, and
wildly underrated postbiotics called short-chain fatty acids. It’s worked for him, it’s worked for his patients,
and it can work for you too.”
—Mahmoud A. Ghannoum, PhD, MBA, author of Total Gut Balance and Director of the
Center for Medical Mycology, Case Western Reserve University
“Although I’ve actively investigated intestinal bacterial functions my entire career, I found Dr. B’s Fiber
Fueled book both highly informative and inspiring. It brings fresh perspectives and very practical solutions
to vexing clinical problems that can be reversed and prevented by incorporating the lifelong healthy eating
patterns described in this transformative book.”
—R. Balfour Sartor, MD, Co-Director, Center for Gastrointestinal Biology and Disease,
Midget Distinguished Professor of Medicine, Microbiology & Immunology, University of North
Carolina School of Medicine
“Fiber Fueled is what happens when you combine almost two decades of medical training, an unrivaled
passion for helping people live healthier, and an incredible ability to break down complex science into easy-
to-digest information for everyone to access. Far more than a diet book—a true master class in gut health
that will be hard to put down.”
—Simon Hill, master’s of nutrition, host of the Plant Proof Podcast, and author of The Proof Is
in the Plants
“At a time when many ‘experts’ are peddling the latest fad diets, Americans are justifiably confused about
what to eat. Will has used his considerable skills to provide an engaging, evidence-based guide that makes it
clear that when you optimize your gut microbiota through diet and lifestyle, you also improve your health.”
—Nicholas J. Shaheen, MD, MPH, Chief of Gastroenterology & Hepatology, Bozymski-Heizer
Distinguished Professor of Medicine, University of North Carolina School of Medicine
“Gastroenterologists should focus on diet and lifestyle to prevent and reverse disease and only use pills and
procedures when these less invasive interventions fail. Dr. Bulsiewicz provides an excellent blueprint in his
book, Fiber Fueled, for a more patient-centered approach to improve overall health.”
—John Pandolfino, MD, MSCI, Chief of Gastroenterology & Hepatology, Hans Popper
Professor of Medicine, Northwestern University
“After many decades of physiological studies evaluating how the GI system works in health and disease, it
is only in the last decade that food, fiber, diet, and the microbiome has found its proper scientific place.
Using his extensive experience, Dr. Bulsiewicz has compiled this new knowledge into a clear and concise
book so that readers having GI illness or who are in health can truly benefit.”
—Douglas A. Drossman, MD, Drossman Gastroenterology, President Emeritus and COO of
the Rome Foundation, and Professor Emeritus of Medicine and Psychiatry, University of North
Carolina School of Medicine
“We live in a country where most people eat twice the recommended daily allowance of protein and almost
no one is eating the recommended fiber. Many think that because we do not absorb fiber it cannot be
important. Dr. Bulsiewicz combines his firsthand knowledge with the available science to teach the reader
the importance of eating varied forms of fiber to feed our varied forms of bacteria residing in our gut, and in
turn improve and prevent both systemic diseases and gut pathology. And if you think your gut just can’t
tolerate fiber, do not fear. The good doctor has a whole chapter dedicated to helping you get over bloating
and other symptoms commonly associated with high-fiber diets.”
—Garth Davis MD, author of Proteinaholic and bariatric surgeon & Medical Director of
Weight Management, Mission Hospital, Asheville, North Carolina
“In a world where most people are obsessed about consuming a lot of protein, this book will revolutionize
the way you think about nutrition. In this evidence-based book, Dr. B delineates the importance of fiber for
great gut health. I recommend for everyone to read this book as great health begins in your gut.”
—Angie Sadeghi, MD, author of The Trifecta of Health
an imprint of Penguin Random House LLC
penguinrandomhouse.com
Copyright © 2020 by Will Bulsiewicz
Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech,
and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying
with copyright laws by not reproducing, scanning, or distributing any part of it in any form without
permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.
ISBN 9780593084564
Ebook ISBN 9780593084571
The recipes contained in this book are to be followed exactly as written. The publisher is not responsible for
your specific health or allergy needs that may require medical supervision. The publisher is not responsible
for any adverse reactions to the recipes contained in this book.
Neither the publisher nor the author is engaged in rendering professional advice or services to the individual
reader. The ideas, procedures, and suggestions contained in this book are not intended as a substitute for
consulting with your physician. All matters regarding your health require medical supervision. Neither the
author nor the publisher shall be liable or responsible for any loss or damage allegedly arising from any
information or suggestion in this book.
pid_prh_5.5.0_c0_r0
I lost my dad during the preparation of this book. It was sudden and completely unexpected.
I couldn’t wait to share this book with him. It would have been easy to just send an electronic copy,
but I really wanted his first read to be a physical book, with the hardcover, all the pages, and his
son’s name on the front.
Over the past few months, my dad repeatedly told me how proud he was of me. He told me that my
grandparents John and Helen Bulsiewicz would have been so proud of the work I was doing in the
name of our family. I can’t tell you how much it means to me that he said all that.
It breaks my heart that he’s not here anymore. I am who I am because of him. But I will forever be
grateful for the special times that we shared.
Love you, Dad. Will always be thinking of you. This book is for you.
Contents
Author’s Note
Introduction
PART I. KNOWLEDGE IS POWER
1. The Engine that Drives Human Health Isn’t Even Human
2. Twenty-First-Century Life: Overfed, Undernourished, and Hyper-
medicated
3. The Fiber Solution: Short-Chain Fatty Acids and Postbiotics for the
Win
PART II. THE FIBER FUELED APPROACH
4. Eat the Rainbow to Find Your Pot of Gold
5. Finding Your Plant Passion with a Sensitive Gut
6. Fermentation Nation Rising
7. Prebiotics, Probiotics, and Postbiotics
8. The Fiber Fueled Foods
PART III. THE FIBER FUELED PLAN
9. Fiber Fueled 365: The Lifestyle
10. The Fiber Fueled 4 Weeks
Acknowledgments
Index
Author’s Note
D
ear Friends,
My goal with this book is to send you off on a journey that transforms your
life. I want you healthier and happier, and I truly believe that the words on these
pages will guide you to that better place.
There was only one way to accomplish my goal, and that was to make this
book a celebration of scientific discovery. We want the laws of nature working
for us, not against us. Science becomes the compass that guides us to that better
place. I share this because you will read this book and hopefully find it
lighthearted and entertaining, but just know that if you pulled back the curtain
you’d discover more than six hundred studies backing up those words.
Legitimate, valid science is the reason accomplished scientists and doctors are
unified in support of this book. You can review all of my references plus more
details about my evidence-based approach at www.theplantfedgut.com/research.
With that said, being Fiber Fueled isn’t a quick fix or a diet; it’s a lifestyle
trajectory that heals. In some cases, those lifestyle choices are optimal when
personalized to your needs and bio-individuality. Therefore, the implementation
of the practices in this book should be done under the guidance of a qualified
health professional to ensure that your specific needs are being met.
Additionally, some of you may want to continue the conversation with me
after reading this book or seek additional resources, and I welcome and celebrate
that. Please join me at www.theplantfedgut.com, where you will find my
podcasts, blog posts, social media channels, free email subscription, and online
course that will allow you to go beyond the book.
Onward to health and happiness together!
Introduction
L
eslie came into my office worn out and exasperated. She was thirty-six years
old, but she felt like she was pushing eighty. She was overweight, a trend that
started in her late twenties while taking the antibiotic minocycline for her acne.
She struggled daily with fatigue, sluggishness, insomnia, and lack of motivation.
Her skin was broken out, her hair was thinning, and she had persistent loose
stools. On top of all this was her extensive list of medical ailments: irritable
bowel, type 2 diabetes, hyperlipidemia, autoimmune thyroiditis, depression, and
anxiety.
After seeing several other GI doctors, a chiropractor, a hormone specialist,
and an expensive cash-only functional doctor, she was confused and frustrated
by the conflicting recommendations. Here she was at thirty-six, on four different
medications with ten supplements to boot. “This isn’t the life I envisioned for
myself,” she told me on that first visit. “I’m way too young to be feeling this
old.”
Much of her frustration stemmed from not knowing what to eat. What should
have been simple had become so complicated. She had gone Paleo in her late
twenties to combat weight gain and she soon progressed to the Whole 30. She
felt better for a short time on those diets, but when the weight gain and fatigue
slowly started to creep back in, she desperately searched for a new diet solution
and tried eliminating phytates and lectins. She’d been gluten-free for almost ten
years and by the time I saw her in my office, she had completely eliminated
grains, legumes, dairy, and nightshades. Her diet now consisted mostly of
arugula, avocado, grass-fed meat, and bone broth, with very little variation. At
times she’d test herself with some beans or whole-wheat bread, but she’d
experience gas and bloating, which the diet gurus she was following warned was
